1. Field of the Invention
The present invention pertains to a method for transporting relatively large quantities of formaldehyde as a methanol-formaldehyde mixture, which may contain water, and which is maintained in a gelled, semi-solid or solid form during transport.
2. Background Art
Aqueous and methanol solutions of formaldehyde are used in relatively large quantities as a biocide for treating water in certain oil and gas production operations. For example, in the production of oil and gas from the Alaskan North Slope oil fields, large quantities of formaldehyde are mixed with the waters which are both injected in and produced from the oil-bearing formations to minimize certain organic activity. Formaldehyde and similar biocides are being considered for use in these applications in similar operations in other parts of the world. The remote location of the treatment facilities where the formaldehyde is injected into the water requires transport of this chemical to its point of injection by both rail and motor truck forms of transportation.
Formaldehyde-methanol-water mixtures are known to form complex mixtures of methylene glycol, methanol-formaldehyde hemiacetal, and their analogous oligimers and polymers as well as small amounts of the three original components. Commercial solutions usually contain minor impurities such as formate, aldol condensates, dimethyl ether, trace corrosion products and other process contaminants. Also additives to inhibit formation and retard precipitation of formaldehyde polymers, are usually present. Formaldehyde solutions are "stabilized" to withstand minimum temperatures and exposure times to eliminate or minimize precipitation of solid phase material. Commercial formaldehyde solutions are stabilized by temperature control, alcohols, dilution, minimized catalytic polymer forming impurities and various additives well known to those skilled in the art. Liquid products marketed for their formaldehyde content are generally solutions containing water, methanol and/or butanol.
Conventional formaldehyde solution transport and storage technology uses solutions dissolved at high temperatures and subsequent formaldehyde polymer precipitation inhibited by methanol, dilution and inhibitory additives well known to the art. These measures slow the precipitation of formaldehyde polymers at moderate temperatures for only a relative short time, usually several months at the manufacturers' minimum recommended temperatures and days or weeks at the conditions on the North Slope of Alaska.
Moreover, it is known that both aqueous and alcoholic solutions of formaldehyde, as used widely in various industrial processes, have upper limits of concentration of the formaldehyde in the solvent to retard precipitation at normal ambient temperatures. Such precipitation is, of course, unwanted in most applications of formaldehyde solutions. On the other hand, the substantial amount of transport required to place large quantities of formaldehyde in the afore-mentioned region for its intended use has raised certain concerns regarding avoidance of uncontained spills during transport and storage. Modification of the product and its method of transport to prevent spillage by gelling the formaldehyde solution will allow the use of transport and storage containers which are larger and are not required to meet overly-strict structural requirements. In other words, the hazards associated with the transport and storage of formaldehyde solutions can be reduced without the additional cost presently associated with transport and handling of this substance. It is to this end that the present invention has been developed with a view to improving certain methods for transporting and storing relatively large quantities of formaldehyde and similar compositions, including their use as biocides.